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 BLIOVLSUS()
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 Purpose:
 Suspend overlay manager operations.

 Syntax:
 BLIOVLSUS(nuLevel)

 Parameters:
 nuLevel  Suspend level.

 Returns:
 None.

 Description:
 This function shuts down the overlay manager. Depending on the level of
 shutdown required, the overlay manager will free up some or all of the
 system resources which it is using. The valid parameters are the numeric
 values 1 through 3, and the system resources freed for each are as
 follows:

 1  Closing all open overlay files, freeing up the DOS handles.
 2  As (1) above, plus freeing of the EMS/XMS used for the overlay cache
 3  Freeing ALL resources used by the overlay manager including the
 overlay pool.

 When the overlay manager is resumed using the BLIOVLRES() function, it will
 attempt to reallocate the same resources it had before. If it is unable to
 reallocate an overlay area, then the program will terminate with a Blinker
 error 1216, 'Overlay manager unable to resume'. If the overlay area is
 reallocated successfully, but there are no resources available for the
 overlay cache, then execution will continue without caching of overlays.
 Note: This routine must be called from the root, as the overlay manager will
 be inactive on return from this call until a call to BLIOVLRES() is made.